vendredi 26 octobre 2012

Astronomers using the NASA/ESA Hubble Space Telescope have obtained a remarkable new view of a whopper of an elliptical galaxy, with a core bigger than any seen before. There are two intriguing explanations for the puffed up core, both related to the action of one or more black holes, and the researchers have not yet been able to determine which is correct.

Spanning a little over one million light-years, the galaxy is about ten times the diameter of the Milky Way galaxy. The bloated galaxy is a member of an unusual class of galaxies with an unusually diffuse core filled without any a concentrated peak of light around a central black hole. Viewing the core is like seeing a city with no centre, just houses sprinkled across a vast landscape.

Monster galaxy lacks a bright core

An international team of astronomers used Hubble's Advanced Camera for Surveys and Wide Field Camera 3 to measure the amount of starlight across the galaxy, catalogued as 2MASX J17222717+3207571 but more commonly called A2261-BCG (short for Abell 2261 Brightest Cluster Galaxy). Located three billion light-years away, the galaxy is the most massive and brightest galaxy in the Abell 2261 cluster.

The Hubble observations revealed that the galaxy's puffy core, measuring about 10 000 light-years, is the largest yet seen. A galaxy's core size is typically correlated with the dimensions of its host galaxy, but in this case, the central region is much larger than astronomers would expect for the galaxy's size. The bloated core is more than three times larger than the centre of other very luminous galaxies.

Astronomers have proposed two possibilities for the puffy core. One scenario is that a pair of merging black holes gravitationally stirred up and scattered the stars. Another idea is that the merging black holes were ejected from the core. Left without an anchor, the stars began spreading out even more, creating the puffy appearance of the core.

Previous Hubble observations have revealed that supermassive black holes, with masses millions or billions times more than the Sun, reside at the centres of nearly all galaxies and may play a role in shaping those central regions.

"Expecting to find a black hole in every galaxy is sort of like expecting to find a pit inside a peach," explains astronomer Tod Lauer of the National Optical Astronomy Observatory in Tucson, USA, a co-author of the Hubble study. "With this Hubble observation, we cut into the biggest peach and we can't find the pit. We don't know for sure that the black hole is not there, but Hubble shows that there's no concentration of stars in the core."

Hubble in orbit

Team leader Marc Postman of the Space Telescope Science Institute in Baltimore, USA, said the galaxy stood out in the Hubble image. "When I first saw the image of this galaxy, I knew right away that it was unusual," Postman explained. "The core was very diffuse and very large. The challenge was then to make sense of all the data, given what we knew from previous Hubble observations, and come up with a plausible explanation for the intriguing nature of this particular galaxy."

The paper describing the results appeared in the 10 September issue of the Astrophysical Journal.

The astronomers expected to see a slight cusp of light in the galaxy's centre, marking the location of the black hole and attendant stars. Instead, the starlight's intensity remained fairly even across the galaxy.

One possibility for the puffy core may be due to two central black holes orbiting each other. These black holes collectively could have been as massive as several billion suns. One of the black holes would be native to the galaxy, while the second could have been added from a smaller galaxy that was gobbled up by the massive elliptical.

In this scenario, stars circling in the giant galaxy's centre came close to the twin black holes. The stars were then given a gravitational boot out of the core. Each gravitational slingshot robbed the black holes of momentum, moving the pair ever closer together, until finally they merged, forming one supermassive black hole that still resides in the galaxy's centre.

Another related possibility is that the black hole merger created gravity waves, which are ripples in the fabric of space. According to the theory of general relativity, a pair of merging black holes produces ripples of gravity that radiate away. If the black holes are of unequal mass, then some of the energy may radiate more strongly in one direction, providing the equivalent of a rocket thrust. The imbalance of forces would have ejected the merged black hole from the centre at speeds of millions of kilometres per hour, resulting in the rarity of a galaxy without a central black hole. "The black hole is the anchor for the stars," Lauer explains. "If you take it out, all of a sudden you have a lot less mass. The stars aren't held together very well and they move outwards, enlarging the core even more."

The team admits that the ejected black-hole scenario may sound far-fetched, "but that's what makes observing the Universe so intriguing — sometimes you find the unexpected," Postman says.

Lauer adds: "This is a system that's interesting enough that it pushes against a lot of questions. We have thought an awful lot about what black holes do. But we haven't been able to test our theories. This is an interesting place where a lot of the ideas we've had can come together and can be tested, fairly exotic ideas about how black holes may interact with each other dynamically and how they would affect the surrounding stellar population."

The team is now conducting follow-up observations with the Very Large Array radio telescope in New Mexico. The astronomers expect material falling onto a black hole to emit radio waves, among other types of radiation. They will compare the VLA data with the Hubble images to more precisely pin down the location of the black hole, if it indeed exists.

The Abell 2261 cluster is part of a multi-wavelength survey, led by Postman, called the Cluster Lensing And Supernova survey with Hubble (CLASH). The survey probes the distribution of dark matter in 25 massive galaxy clusters.

Notes:

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

jeudi 25 octobre 2012

A second look at data from NASA's Hubble Space Telescope is reanimating the claim that the nearby star Fomalhaut hosts a massive exoplanet. The study suggests that the planet, named Fomalhaut b, is a rare and possibly unique object that is completely shrouded by dust.

Fomalhaut is the brightest star in the constellation Piscis Austrinus and lies 25 light-years away.

Hubble Space Telescope. Credit: NASA/ESA

In November 2008, Hubble astronomers announced the exoplanet, named Fomalhaut b, as the first one ever directly imaged in visible light around another star. The object was imaged just inside a vast ring of debris surrounding but offset from the host star. The planet's location and mass -- no more than three times Jupiter's -- seemed just right for its gravity to explain the ring's appearance.

Recent studies have claimed that this planetary interpretation is incorrect. Based on the object's apparent motion and the lack of an infrared detection by NASA's Spitzer Space Telescope, they argue that the object is a short-lived dust cloud unrelated to any planet.

A new analysis, however, brings the planet conclusion back to life.

Video above: In 2008, Hubble astronomers announced the detection of a giant planet around the bright star Fomalhaut. Recent studies have questioned this conclusion. Now, a reanalysis of Hubble data has revived the "deceased" exoplanet as a dust-shrouded world with less than twice the mass of Jupiter. (Credit: NASA's Goddard Space Flight Center).

NASA's Spitzer Space Telescope. Credit: NASA/JPL-Caltech

"Although our results seriously challenge the original discovery paper, they do so in a way that actually makes the object's interpretation much cleaner and leaves intact the core conclusion, that Fomalhaut b is indeed a massive planet," said Thayne Currie, an astronomer formerly at NASA's Goddard Space Flight Center in Greenbelt, Md., and now at the University of Toronto.

The discovery study reported that Fomalhaut b's brightness varied by about a factor of two and cited this as evidence that the planet was accreting gas. Follow-up studies then interpreted this variability as evidence that the object actually was a transient dust cloud instead.

In the new study, Currie and his team reanalyzed Hubble observations of the star from 2004 and 2006. They easily recovered the planet in observations taken at visible wavelengths near 600 and 800 nanometers, and made a new detection in violet light near 400 nanometers. In contrast to the earlier research, the team found that the planet remained at constant brightness.

The team attempted to detect Fomalhaut b in the infrared using the Subaru Telescope in Hawaii, but was unable to do so. The non-detections with Subaru and Spitzer imply that Fomalhaut b must have less than twice the mass of Jupiter.

Another contentious issue has been the object's orbit. If Fomalhaut b is responsible for the ring's offset and sharp interior edge, then it must follow an orbit aligned with the ring and must now be moving at its slowest speed. The speed implied by the original study appeared to be too fast. Additionally, some researchers argued that Fomalhaut b follows a tilted orbit that passes through the ring plane.

Using the Hubble data, Currie's team established that Fomalhaut b is moving with a speed and direction consistent with the original idea that the planet's gravity is modifying the ring.

Image above: This visible-light image from the Hubble Space Telescope shows the vicinity of the star Fomalhaut, including the location of its dust ring and disputed planet, Fomalhaut b. A coronagraphic mask helped dim the star's brightness. This view combines two 2006 observations that were taken with masks of different sizes (1.8 and 3 arcseconds). (Credit: NASA/ESA/T. Currie, U. Toronto).

"What we've seen from our analysis is that the object's minimum distance from the disk has hardly changed at all in two years, which is a good sign that it's in a nice ring-sculpting orbit," explained Timothy Rodigas, a graduate student in the University of Arizona and a member of the team.

Currie's team also addressed studies that interpret Fomalhaut b as a compact dust cloud not gravitationally bound to a planet. Near Fomalhaut's ring, orbital dynamics would spread out or completely dissipate such a cloud in as little as 60,000 years. The dust grains experience additional forces, which operate on much faster timescales, as they interact with the star's light.

"Given what we know about the behavior of dust and the environment where the planet is located, we think that we're seeing a planetary object that is completely embedded in dust rather than a free-floating dust cloud," said team member John Debes, an astronomer at the Space Telescope Science Institute in Baltimore, Md.

A paper describing the findings has been accepted for publication in The Astrophysical Journal Letters.

Because astronomers detect Fomalhaut b by the light of surrounding dust and not by light or heat emitted by its atmosphere, it no longer ranks as a "directly imaged exoplanet." But because it's the right mass and in the right place to sculpt the ring, Currie's team thinks it should be considered a "planet identified from direct imaging."

Fomalhaut was targeted with Hubble most recently in May by another team. Those observations are currently under scientific analysis and are expected to be published soon.

Notes:The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

One of the lowest mass supermassive black holes ever observed in the middle of a galaxy has been identified, thanks to NASA's Chandra X-ray Observatory and several other observatories. The host galaxy is of a type not expected to harbor supermassive black holes, suggesting that this black hole, while related to its supermassive cousins, may have a different origin.

The black hole is located in the middle of the spiral galaxy NGC 4178, shown in this image from the Sloan Digital Sky Survey. The inset shows an X-ray source at the position of the black hole, in the center of a Chandra image. An analysis of the Chandra data, along with infrared data from NASA's Spitzer Space Telescope and radio data from the NSF's Very Large Array suggests that the black hole is near the extreme low-mass end of the supermassive black hole range.

These results were published in the July 1, 2012 issue of The Astrophysical Journal by Nathan Secrest, from George Mason University in Fairfax, Virginia, and collaborators.

The properties of the X-ray source, including its brightness and spectrum - the amount of X-rays at different wavelengths - and its brightness at infrared wavelengths, suggest that a black hole in the center of NGC 4178 is rapidly pulling in material from its surroundings. The same data also suggest that light generated by this infalling material is heavily absorbed by gas and dust surrounding the black hole.

Chandra X-ray Observatory

A known relationship between the mass of a black hole and the amount of X-rays and radio waves it generates was used to estimate the mass of the black hole. This method gives a black hole mass estimate of less than about 200,000 times that of the sun. This agrees with mass estimates from several other methods employed by the authors, and is lower than the typical values for supermassive black holes of millions to billions of times the mass of the sun.

NGC 4178 is a spiral galaxy located about 55 million light years from Earth. It does not contain a bright central concentration, or bulge, of stars in its center. Besides NGC 4178, four other galaxies without bulges are currently thought to contain supermassive black holes. Of these four black holes, two have masses that may be close to that of the black hole in NGC 4178. XMM-Newton observations of an X-ray source discovered by Chandra in the center of the galaxy NGC 4561 indicate that the mass of this black hole is greater than 20,000 times the mass of the sun, but the mass could be substantially higher if the black hole is pulling in material slowly, causing it to generate less X-ray emission. A paper describing these results was published in the October 1st, 2012 issue of The Astrophysical Journal by Araya Salvo and collaborators.

The mass of the black hole in the galaxy NGC 4395 is estimated to be about 360,000 times the mass of the sun, as published by Peterson and collaborators in the October 20, 2005 issue of the Astrophysical Journal.

The heat-seeking capabilities of the international Cassini spacecraft and two ground-based telescopes have provided the first look at the aftermath of Saturn’s ‘Great Springtime Storm’. Concealed from the naked eye, a giant oval vortex is persisting long after the visible effects of the storm subsided.

The ground-based observations were made by the Very Large Telescope of the European Southern Observatory in Chile, and NASA’s Infrared Telescope Facility at the summit of Mauna Kea in Hawaii.

Saturn’s visible storm

The vivid cloud structures that wreaked havoc across wide swathes of the mid-northern latitudes of Saturn’s atmosphere captured the imaginations of amateur and professional astronomers alike, from its first appearance in December 2010 through much of 2011.

But in new reports that focus on the temperatures, winds and composition of Saturn’s atmosphere, scientists find that the spectacular cloud displays were only part of the story.

Much of the associated activity took place beyond the reach of visible-light cameras, and the after-effects are still continuing today.

Evolution of infrared hotspots in Saturn’s springtime storm

“It’s the first time we’ve seen anything like it on any planet in the Solar System,” says Leigh Fletcher from the University of Oxford, UK, lead author of the Icarus paper.

“It’s extremely unusual, as we can only see the vortex at infrared wavelengths – we can’t tell that it is there simply by looking at the cloud cover.”

As the visible storm erupted in the roiling cloud deck of Saturn’s troposphere, waves of energy rippled hundreds of kilometres upwards, depositing their energy as two vast ‘beacons’ of hot air in the stratosphere.

The beacons were expected to cool down and dissipate, but by late April 2011 – by which time bright cloud material had encircled the entire planet – the hot spots had merged to create an enormous vortex that for a brief period exceeded even the size of Jupiter’s famous Great Red Spot.

Furthermore, the temperature of the vortex was far higher than expected, some 80ºC warmer than the surrounding atmosphere. At the same time, huge spikes in the amount of gases like ethylene and acetylene were detected.

Looking down on Saturn’s storm

Much like the Great Red Spot, Saturn’s vortex also cuts off the atmosphere in its core from the surrounding environment, constraining its unique chemistry and high temperatures within the walls of the powerful winds whipping around the edge.

“But Jupiter’s vortex is embedded deep down in the turbulent ‘weather zone’, whereas the vast vortex on Saturn is higher up in the atmosphere where, normally, you wouldn’t expect anything like it to have formed,” says Dr Fletcher.

“Although there are parallels to be drawn between the two, the mechanisms by which they were formed and the length of time they are going to exist seem to be very different.”

Jupiter’s famous vortex has raged for at least 300 years, but after traversing the planet once every 120 days since May 2011, Saturn’s large beacon is cooling and shrinking. Scientists expect it to fade away completely by the end of 2013.

Storm on Saturn

The question now remains as to whether Saturn’s storm-generating energy has been sapped or if there will be a repeat performance.

The outburst already caught observers by surprise by arriving during the planet’s northern hemisphere spring, years ahead of the predictably stormy summer season.

“The beauty is that Cassini will be operating until the Saturn system reaches its summer solstice in 2017, so if there is another global event like this, we’ll be there to see it,” says ESA’s Cassini project scientist Nicolas Altobelli.

According to the program of space flight on October 25 in 16 hours 29 minutes Moscow time carried out docking of manned spacecraft (TPC) Soyuz TMA-06M to the International Space Station (ISS).

The spacecraft docked with the small research module "Search". Convergence process was carried out in automatic mode under the supervision of specialists in the Mission Control Center (Korolev, Moscow Region.) And the ISS crew.

Soyuz TMA-06M Docks to ISS

Run TMC Soyuz TMA-06M was held on October 23 at 14:51 Moscow time from the launch complex of the platform 31 at Baikonur. On the ship to the International Space Station crew launched in the Russian Federal Space Agency cosmonaut Oleg Novitsky, Eugene Tarelkin and NASA astronaut Kevin Ford.

Prior to the opening of hatches and go to the ISS crew TPK Soyuz TMA-06M will control the ship watertight compartments, move into consumer compartment where withdraw and space suits and will equalize between the station and the ship.

Hatches between the International Space Station and the Soyuz will open in a couple of hours after pressure and leak checks.

Ford’s last mission was as a pilot aboard space shuttle Discovery in 2009 during the STS-128 flight to the space station. The two week mission delivered experiments and gear inside the Leonardo multi-purpose module and exchanged two Expedition 20 crew members.

This is the first spaceflight for both Novitskiy and Tarelkin.

ISS - Expedition 33 Crew portrait

Expedition 33 will be a six-member crew until Nov. 12 when Williams, Hoshide and Malenchenko undock from the Rassvet module and return home inside the Soyuz TMA-05M spacecraft for a landing in Kazakhstan. When they undock Expedition 34 will officially begin as Ford becomes commander staying behind with Novitskiy and Tarelkin finally returning home in March 2013.

Back on Earth three more crew members are in Star City, Russia, training for their Dec. 5 launch to return the station to a six-member crew. Veteran astronauts Chris Hadfield and Tom Marshburn along with veteran cosmonaut Roman Romanenko will complete the Expedition 34 crew. They will start the Expedition 35 crew beginning in March.

The average area covered by the Antarctic ozone hole this year was the second smallest in the last 20 years, according to data from NASA and National Oceanic and Atmospheric Administration (NOAA) satellites. Scientists attribute the change to warmer temperatures in the Antarctic lower stratosphere.

The ozone hole reached its maximum size Sept. 22, covering 8.2 million square miles (21.2 million square kilometers), or the area of the United States, Canada and Mexico combined. The average size of the 2012 ozone hole was 6.9 million square miles (17.9 million square kilometers). The Sept. 6, 2000 ozone hole was the largest on record at 11.5 million square miles (29.9 million square kilometers).

"The ozone hole mainly is caused by chlorine from human-produced chemicals, and these chlorine levels are still sizable in the Antarctic stratosphere," said NASA atmospheric scientist Paul Newman of NASA's Goddard Space Flight Center in Greenbelt, Md. "Natural fluctuations in weather patterns resulted in warmer stratospheric temperatures this year. These temperatures led to a smaller ozone hole."

Observing Earth's Ozone Layer

Video above: Atmospheric ozone is no longer declining because concentrations of ozone-depleting chemicals stopped increasing and are now declining.

The ozone layer acts as Earth's natural shield against ultraviolet radiation, which can cause skin cancer. The ozone hole phenomenon began making a yearly appearance in the early 1980s. The Antarctic ozone layer likely will not return to its early 1980s state until about 2065, Newman said. The lengthy recovery is because of the long lifetimes of ozone-depleting substances in the atmosphere. Overall atmospheric ozone no longer is declining as concentrations of ozone-depleting substances decrease. The decrease is the result of an international agreement regulating the production of certain chemicals.

The ozone hole max on Sept. 22, 2012

This year also marked a change in the concentration of ozone over the Antarctic. The minimum value of total ozone in the ozone hole was the second highest level in two decades. Total ozone, measured in Dobson units (DU) reached 124 DU on Oct. 1. NOAA ground-based measurements at the South Pole recorded 136 DU on Oct. 5. When the ozone hole is not present, total ozone typically ranges from 240-500 DU.

This is the first year growth of the ozone hole has been observed by an ozone-monitoring instrument on the Suomi National Polar-orbiting Partnership (NPP) satellite. The instrument, called the Ozone Mapping Profiler Suite (OMPS), is based on previous instruments, such as the Total Ozone Mapping Spectrometer (TOMS) and the Solar Backscatter Ultraviolet instrument (SBUV/2). OMPS continues a satellite record dating back to the early 1970s.

This image shows projected ozone concentrations for the year 2042, with (left) and without (right) the Montreal Protocol to reduce CFCs begun in the 1980s.

In addition to observing the annual formation and extent of the ozone hole, scientists hope OMPS will help them better understand ozone destruction in the middle and upper stratosphere with its Nadir Profiler. Ozone variations in the lower stratosphere will be measured with its Limb Profiler.

"OMPS Limb looks sideways, and it can measure ozone as a function of height," said Pawan K. Bhartia, a NASA atmospheric physicist and OMPS Limb instrument lead. "This OMPS instrument allows us to more closely see the vertical development of Antarctic ozone depletion in the lower stratosphere where the ozone hole occurs."

Suomi National Polar-orbiting Partnership (NPP) satellite

NASA and NOAA have been monitoring the ozone layer on the ground and with a variety of instruments on satellites and balloons since the 1970s. Long-term ozone monitoring instruments have included TOMS, SBUV/2, Stratospheric Aerosol and Gas Experiment series of instruments, the Microwave Limb Sounder, the Ozone Monitoring Instrument, and the OMPS instrument on Suomi NPP. Suomi NPP is a bridging mission leading to the next-generation polar-orbiting environmental satellites called the Joint Polar Satellite System, will extend ozone monitoring into the 2030s.

NASA and NOAA have a mandate under the Clean Air Act to monitor ozone-depleting gases and stratospheric depletion of ozone. NOAA complies with this mandate by monitoring ozone via ground and satellite measurements. The NOAA Earth System Research Laboratory in Boulder, Colo., performs the ground-based monitoring. The Climate Prediction Center performs the satellite monitoring.

A new study using data from NASA's Spitzer Space Telescope suggests a cause for the mysterious glow of infrared light seen across the entire sky. It comes from isolated stars beyond the edges of galaxies. These stars are thought to have once belonged to the galaxies before violent galaxy mergers stripped them away into the relatively empty space outside of their former homes.

"The infrared background glow in our sky has been a huge mystery," said Asantha Cooray of the University of California at Irvine, lead author of the new research published in the journal Nature. "We have new evidence this light is from the stars that linger between galaxies. Individually, the stars are too faint to be seen, but we think we are seeing their collective glow."

Image above: New research from scientists using NASA's Spitzer Space Telescope suggests that a mysterious infrared glow across our whole sky is coming from stray stars torn from galaxies, which is shown in this artist's concept. Image credit: NASA/JPL-Caltech.

The findings disagree with another theory explaining the same background infrared light observed by Spitzer. A group led by Alexander "Sasha" Kashlinsky of NASA's Goddard Space Flight Center in Greenbelt, Md., proposed in June this light, which appears in Spitzer images as a blotchy pattern, is coming from the very first stars and galaxies.

In the new study, Cooray and colleagues looked at data from a larger portion of the sky, called the Bootes field, covering an arc equivalent to 50 full Earth moons. These observations were not as sensitive as those from the Kashlinsky group's studies, but the larger scale allowed researchers to analyze better the pattern of the background infrared light.

"We looked at the Bootes field with Spitzer for 250 hours," said co-author Daniel Stern of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Studying the faint infrared background was one of the core goals of our survey, and we carefully designed the observations in order to directly address the important, challenging question of what causes the background glow."

The image on the left shows a portion of our sky, called the Boötes field, in infrared light, while the image on the right shows a mysterious, background infrared glow captured by NASA's Spitzer Space Telescope in the same region of sky. Image credit: NASA/JPL-Caltech/Carnegie.

The team concluded the light pattern of the infrared glow is not consistent with theories and computer simulations of the first stars and galaxies. Researchers say the glow is too bright to be from the first galaxies, which are thought not to have been as large or as numerous as the galaxies we see around us today. Instead, the scientists propose a new theory to explain the blotchy light, based on theories of "intracluster" or "intrahalo" starlight.

Theories predict a diffuse smattering of stars beyond the halos, or outer reaches, of galaxies, and in the spaces between clusters of galaxies. The presence of these stars can be attributed to two phenomena. Early in the history of our universe as galaxies grew in size, they collided with other galaxies and gained mass. As the colliding galaxies became tangled gravitationally, strips of stars were shredded and tossed into space. Galaxies also grow by swallowing smaller dwarf galaxies, a messy process that also results in stray stars.

"A light bulb went off when reading some research papers predicting the existence of diffuse stars," Cooray said. "They could explain what we are seeing with Spitzer."

More research is needed to confirm this sprinkling of stars makes up a significant fraction of the background infrared light. For instance, it would be necessary to find a similar pattern in follow-up observations in visible light. NASA's upcoming James Webb Space Telescope (JWST) might finally settle the matter for good.

SPITZER Space Telescope

"The keen infrared vision of the James Webb Telescope will be able to see some of the earliest stars and galaxies directly, as well as the stray stars lurking between the outskirts of nearby galaxies," said Eric Smith, JWST's deputy program manager at NASA Headquarters in Washington. "The mystery objects making up the background infrared light may finally be exposed."

Other authors include Joseph Smidt, Francesco De Bernardis, Yan Gong and Christopher C. Frazer of UC Irvine; Matthew L. N. Ashby of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass; Peter R. Eisenhardt of JPL; Anthony H. Gonzalez of the University of Florida in Gainesville; Christopher S. Kochanek of Ohio State University in Columbus; Szymon Kozłowski of Ohio State and the Warsaw University Observatory in Poland; and Edward L. Wright of the University of California, Los Angeles.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

ESA’s quartet of satellites studying Earth’s magnetosphere, Cluster, has discovered that our protective magnetic bubble lets the solar wind in under a wider range of conditions than previously believed.

Earth’s magnetic field is our planet’s first line of defence against the bombardment of the solar wind. This stream of plasma is launched by the Sun and travels across the Solar System, carrying its own magnetic field with it.

Depending on how the solar wind’s interplanetary magnetic field – IMF – is aligned with Earth’s magnetic field, different phenomena can arise in Earth’s immediate environment.

Solar wind entry at low latitudes

One well-known process is magnetic reconnection, where magnetic field lines pointing in opposite directions spontaneously break and reconnect with other nearby field lines. This redirects their plasma load into the magnetosphere, opening the door to the solar wind and allowing it to reach Earth.

In 2006, Cluster made the surprising discovery that huge, 40 000 km swirls of plasma along the boundary of the magnetosphere – the magnetopause – could allow the solar wind to enter, even when Earth’s magnetic field and the IMF are aligned.

These swirls were found at low, equatorial latitudes, where the magnetic fields were most closely aligned.

These giant vortices are driven by a process known as the Kelvin–Helmholtz (KH) effect, which can occur anywhere in nature when two adjacent flows slip past each other at different speeds.

Examples include waves whipped up by wind sliding across the surface of the ocean, or in atmospheric clouds.

Solar wind entry at high latitudes

Analysis of Cluster data has now found that KH waves can also occur at a wider range of magnetopause locations and when the IMF is arranged in a number of other configurations, providing a mechanism for the continuous transport of the solar wind into Earth’s magnetosphere.

“We found that when the interplanetary magnetic field is westward or eastward, magnetopause boundary layers at higher latitude become most subject to KH instabilities, regions quite distant from previous observations of these waves,” says Kyoung-Joo Hwang of NASA’s Goddard Space Flight Center and lead author of the paper published in the Journal of Geophysical Research.

“In fact, it’s very hard to imagine a situation where solar wind plasma could not leak into the magnetosphere, since it is not a perfect magnetic bubble.”

The findings confirm theoretical predictions and are reproduced by simulations presented by the authors of the new study.

“The solar wind can enter the magnetosphere at different locations and under different magnetic field conditions that we hadn’t known about before,” says co-author Melvyn Goldstein, also from Goddard Space Flight Center.

ESA's four Cluster's in orbit (Artist view)

“That suggests there is a ‘sieve-like’ property of the magnetopause in allowing the solar wind to continuously flow into the magnetosphere.”

The KH effect is also seen in the magnetospheres of Mercury and Saturn, and the new results suggest that it may provide a possible continuous entry mechanism of solar wind into those planetary magnetospheres, too.

“Cluster’s observations of these boundary waves have provided a great advance on our understanding of solar wind – magnetosphere interactions, which are at the heart of space weather research,” says Matt Taylor, ESA’s Cluster project scientist.

“In this case, the relatively small separation of the four Cluster satellites as they passed through the high-latitude dayside magnetopause provided a microscopic look at the processes ripping open the magnetopause and allowing particles from the Sun direct entry into the atmosphere.”

Using a whopping nine-gigapixel image from the VISTA infrared survey telescope at ESO’s Paranal Observatory, an international team of astronomers has created a catalogue of more than 84 million stars in the central parts of the Milky Way. This gigantic dataset contains more than ten times more stars than previous studies and is a major step forward for the understanding of our home galaxy. The image gives viewers an incredible, zoomable view of the central part of our galaxy. It is so large that, if printed with the resolution of a typical book, it would be 9 metres long and 7 metres tall.

Wide-field view of the Milky Way, showing the extent of a new VISTA gigapixel image

“By observing in detail the myriads of stars surrounding the centre of the Milky Way we can learn a lot more about the formation and evolution of not only our galaxy, but also spiral galaxies in general,” explains Roberto Saito (Pontificia Universidad Católica de Chile, Universidad de Valparaíso and The Milky Way Millennium Nucleus, Chile), lead author of the study.

Optical/infrared comparison of the central parts of the Milky Way

Most spiral galaxies, including our home galaxy the Milky Way, have a large concentration of ancient stars surrounding the centre that astronomers call the bulge. Understanding the formation and evolution of the Milky Way’s bulge is vital for understanding the galaxy as a whole. However, obtaining detailed observations of this region is not an easy task.

“Observations of the bulge of the Milky Way are very hard because it is obscured by dust,” says Dante Minniti (Pontificia Universidad Catolica de Chile, Chile), co-author of the study. “To peer into the heart of the galaxy, we need to observe in infrared light, which is less affected by the dust.”

Colour–magnitude diagram of the Galactic bulge

The large mirror, wide field of view and very sensitive infrared detectors of ESO’s 4.1-metre Visible and Infrared Survey Telescope for Astronomy (VISTA) make it by far the best tool for this job. The team of astronomers is using data from the VISTA Variables in the Via Lactea programme (VVV) [1], one of six public surveys carried out with VISTA. The data have been used to create a monumental 108 200 by 81 500 pixel colour image containing nearly nine billion pixels. This is one of the biggest astronomical images ever produced. The team has now used these data to compile the largest catalogue of the central concentration of stars in the Milky Way ever created [2].

Annotated map of VISTA’s view of the centre of the Milky Way

To help analyse this huge catalogue the brightness of each star is plotted against its colour for about 84 million stars to create a colour–magnitude diagram. This plot contains more than ten times more stars than any previous study and it is the first time that this has been done for the entire bulge. Colour–magnitude diagrams are very valuable tools that are often used by astronomers to study the different physical properties of stars such as their temperatures, masses and ages [3].

“Each star occupies a particular spot in this diagram at any moment during its lifetime. Where it falls depends on how bright it is and how hot it is. Since the new data gives us a snapshot of all the stars in one go, we can now make a census of all the stars in this part of the Milky Way,” explains Dante Minniti.

Video above: Infrared/visible light comparison of VISTA’s gigapixel view of the centre of the Milky Way.

The new colour–magnitude diagram of the bulge contains a treasure trove of information about the structure and content of the Milky Way. One interesting result revealed in the new data is the large number of faint red dwarf stars. These are prime candidates around which to search for small exoplanets using the transit method [4].

“One of the other great things about the VVV survey is that it’s one of the ESO VISTA public surveys. This means that we’re making all the data publicly available through the ESO data archive, so we expect many other exciting results to come out of this great resource," concludes Roberto Saito.

Notes:

[1] The VISTA Variables in the Via Lactea (VVV) survey is an ESO public survey dedicated to scanning the southern plane and bulge of the Milky Way through five near-infrared filters. It started in 2010 and was granted a total of 1929 hours of observing time over a five-year period. Via Lactea is the Latin name for the Milky Way.

[2] The image used in this work covers about 315 square degrees of the sky (a bit less than 1% of the entire sky) and observations were carried out using three different infrared filters. The catalogue lists the positions of the stars along with their measured brightnesses through the different filters. It contains about 173 million objects, of which about 84 million have been confirmed as stars. The other objects were either too faint or blended with their neighbours or affected by other artefacts, so that accurate measurements were not possible. Others were extended objects such as distant galaxies.

The image used here required a huge amount of data processing, which was performed by Ignacio Toledo at the ALMA OSF. It corresponds to a pixel scale of 0.6 arcseconds per pixel, down-sampled from the original pixel scale of 0.34 arcseconds per pixel.

[3] A colour–magnitude diagram is a graph that plots the apparent brightnesses of a set of objects against their colours. The colour is measured by comparing how bright objects look through different filters. It is similar to a Hertzsprung-Russell (HR) diagram but the latter plots luminosity (or absolute magnitude) rather than just apparent brightness and a knowledge of the distances of the stars plotted is also needed.

[4] The transit method for finding planets searches for the small drop in brightness of a star that occurs when a planet passes in front of it and blocks some of its light. The small size of the red dwarf stars, typically with spectral types K and M, gives a greater relative drop in brightness when low-mass planets pass in front of them, making it easier to search for planets around them.

More information:This research was presented in a paper “Milky Way Demographics with the VVV Survey I. The 84 Million Star Colour–Magnitude Diagram of the Galactic Bulge“ by R. K. Saito et al., which was published in the journal Astronomy & Astrophysics (A&A, 544, A147).

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

NASA's newest set of X-ray eyes in the sky, the Nuclear Spectroscopic Telescope Array (NuSTAR), has caught its first look at the giant black hole parked at the center of our galaxy. The observations show the typically mild-mannered black hole during the middle of a flare-up.

"We got lucky to have captured an outburst from the black hole during our observing campaign," said Fiona Harrison, the mission's principal investigator at the California Institute of Technology (Caltech) in Pasadena. "These data will help us better understand the gentle giant at the heart of our galaxy and why it sometimes flares up for a few hours and then returns to slumber."

NuSTAR, launched June 13, is the only telescope capable of producing focused images of the highest-energy X-rays. For two days in July, the telescope teamed up with other observatories to observe Sagittarius A* (pronounced Sagittarius A-star and abbreviated Sgr A*), the name astronomers give to a compact radio source at the center of the Milky Way. Observations show a massive black hole lies at this location. Participating telescopes included NASA's Chandra X-ray Observatory, which sees lower-energy X-ray light; and the W.M. Keck Observatory atop Mauna Kea in Hawaii, which took infrared images.

Compared to giant black holes at the centers of other galaxies, Sgr A* is relatively quiet. Active black holes tend to gobble up stars and other fuel around them. Sgr A* is thought only to nibble or not eat at all, a process that is not fully understood. When black holes consume fuel -- whether a star, a gas cloud or, as recent Chandra observations have suggested, even an asteroid -- they erupt with extra energy.

In the case of NuSTAR, its state-of-the-art telescope is picking up X-rays emitted by consumed matter being heated up to about 180 million degrees Fahrenheit (100 million degrees Celsius) and originating from regions where particles are boosted very close to the speed of light. Astronomers say these NuSTAR data, when combined with the simultaneous observations taken at other wavelengths, will help them better understand the physics of how black holes snack and grow in size.

Image above: These are the first, focused high-energy X-ray views of the area surrounding the supermassive black hole, called Sagittarius A*, at the center of our galaxy. Image credit: NASA/JPL-Caltech.

"Astronomers have long speculated that the black hole's snacking should produce copious hard X-rays, but NuSTAR is the first telescope with sufficient sensitivity to actually detect them," said NuSTAR team member Chuck Hailey of Columbia University in New York City.

NuSTAR is a Small Explorer mission led by Caltech and managed by NASA's Jet Propulsion Laboratory in Pasadena for NASA's Science Mission Directorate in Washington. Orbital Sciences Corporation of Dulles, Va., built the spacecraft. Its instrument was built by a consortium including Caltech; JPL; the University of California (UC) Berkeley; Columbia University; NASA's Goddard Space Flight Center in Greenbelt, Md.; the Danish Technical University in Denmark; Lawrence Livermore National Laboratory in Livermore, Calif.; and ATK Aerospace Systems of Goleta, Calif.

NuSTAR's mission operations center is at UC Berkeley, with the Italian Space Agency providing an equatorial ground station located at Malindi, Kenya. The mission's outreach program is based at Sonoma State University in Rohnert Park, Calif. Goddard manages NASA's Explorer Program. Caltech manages JPL for NASA.

NASA astronaut Kevin Ford and Russian cosmonauts Evgeny Tarelkin and Oleg Novitskiy launched aboard a Russian Soyuz rocket on their mission to the International Space Station at 5:51 a.m. CDT Tuesday (4:51 p.m. Kazakhstan time). The trio lifted off from Site 31 at the Baikonur Cosmodrome in Kazakhstan. This is the first time in 28 years the pad has been used for human spaceflight.

New Trio Launches to Join Expedition 33

Ford, Tarelkin and Novitskiy will spend the next two days inside their Soyuz TMA-06M spacecraft as they close in on the space station. Novitskiy is serving as the commander of the Soyuz and will be at the controls as the spacecraft docks with the Poisk module of the station Thursday. The three will join Expedition 33 Commander Sunita Williams of NASA and Flight Engineers Aki Hoshide of the Japan Aerospace Exploration Agency and Yuri Malenchenko of the Russian Federal Space Agency, who have been living aboard the orbiting laboratory since July.

Expedition 33 liftoff

NASA TV will provide live coverage of the Soyuz docking beginning at 7 a.m. CDT (8 a.m. EDT) Thursday. Coverage of the hatch opening and welcome ceremony aboard the space station will begin at 9:45 a.m. Hatch opening is scheduled for approximately 10:15 a.m.

Ford, Novitskiy and Tarelkin will remain aboard the station until March 2013. Williams, Malenchenko and Hoshide will return to Earth Nov. 19. When Williams, Malenchenko and Hoshide undock from the station, it will signal the end of Expedition 33 and the beginning of Expedition 34 with Ford as commander.

lundi 22 octobre 2012

This week, scientists from CERN participated in a meeting organized by Wilton Park organization, held near Geneva, from 15 to 18 October. Eminent personalities were invited to consider different worldviews from science, philosophy and theology, and to reflect that these visions were shared. Is it possible to develop a common language for meaningful dialogue?

Wilton Park is an organization designed to provide a framework for discussion and reflection on the major political issues worldwide, bringing together experts from around the world to discuss current topics. More than 50 events are organized each year by this structure, which is a neutral environment in which divergent views can be expressed and confront calmly.

The meeting, organized in partnership with CERN, has enabled scientists from different disciplines to engage in dialogue with philosophers and theologians of different faiths on the nature of the Big Bang theory. A report and an electronic book will be published later.

Note:
CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.

The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.

Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 20 Member States.

Earth’s Grand Canyon inspires awe for anyone who casts eyes upon the vast river-cut valley, but it would seem nothing more than a scratch next to the cavernous scar of Valles Marineris that marks the face of Mars.

Stretching over 4000 km long and 200 km wide, and with a dizzying depth of 10 km, it is some ten times longer and five times deeper than Earth’s Grand Canyon, a size that earns it the status of the largest canyon in the Solar System.

Seen here in new light and online for the first time, this bird’s-eye view of Valles Marineris was created from data captured during 20 individual orbits of ESA’s Mars Express. It is presented in near-true colour and with four times vertical exaggeration.

A wide variety of geological features can be seen, reflecting the complex geological history of the region.

The canyon’s formation is likely intimately linked with the formation of the neighbouring Tharsis bulge, which is out of shot and to the left of this image and home to the largest volcano in the Solar System, Olympus Mons.

The volcanic activity is revealed by the nature of the rocks in the walls of the canyon and the surrounding plains, which were built by successive lava flows.

ESA's Mars Express

As the Tharsis bulge swelled with magma during the planet’s first billion years, the surrounding crust was stretched, ripping apart and eventually collapsing into the gigantic troughs of Valles Marineris.

Intricate fault patterns have also developed due to the imposing extensional forces; the most recent are particularly evident in the middle portion of the image and along the lower boundary of the frame.

Landslides have also played a role in shaping the scene, especially in the northern-most troughs, where material has recently slumped down the steep walls. Mass wasting has also created delicate erosion of the highest part of the walls.

Strong water flows may have reshaped Valles Marineris after it was formed, deepening the canyon. Mineralogical information collected by orbiting spacecraft, including Mars Express, shows that the terrain here was altered by water hundreds of millions of years ago.